The disclosure relates to a hydrostatic axial piston machine configured as a hydraulic pump or as a hydraulic motor or configured to be operated both as a hydraulic pump and as a hydraulic motor.
Axial piston machines are known, in which the cylinder barrel and a control plate (also called control disk) lie on one another with planar bearing faces, and the cylinder bores and/or the working pistons which are mounted displaceably therein are arranged parallel to the rotational axis of the drive shaft, as is disclosed, for example, in DE 10 2010 006 895 A1. It is also known to design the bearing faces of the cylinder barrel and control plate to be spherical and to arrange the cylinder bores and the working pistons parallel to the rotational axis of the drive shaft, as shown, for example, in DE 34 13 059 C1 (FIG. 1) or in DE 197 06 263 C1. Furthermore, it is known to design the bearing faces of the cylinder drum and control plate to be spherical and to arrange the cylinder bores and the working pistons obliquely with respect to the rotational axis of the drive shaft, cylinder bores approaching the rotational axis radially in the direction of the bearing face, as disclosed, for example, in DE 34 13 059 C1 (FIGS. 2 and 3) or in DE 10 2008 012 593 A1. Finally, it is known to design the bearing faces of the cylinder drum and control plate to be planar and to arrange the cylinder bores and the working pistons obliquely with respect to the rotational axis of the drive shaft, as is disclosed, for example, in GB 1 073 216 or in DE 40 35 748 A1 (FIG. 2).
During the passage of a working pressure medium from an inlet line of an axial piston machine through a control opening in the control plate and into a cylinder bore which is delimited in sections by a working piston, that is to say into the working space, the working pressure medium is accelerated to a very pronounced extent on account of the high circumferential speed of the working spaces in the cylinder barrel which optionally also rotates rapidly. As a consequence, known axial piston machines reach the cavitation range during operation at high rotational speeds and are limited with regard to the rotational speed which can be achieved. This problem can be reduced if the inlet openings of the working spaces are arranged closer to the rotational axis of the cylinder barrel, that is to say radially further to the inside, because the circumferential speed also decreases together with the radius. In this regard, constructions of the cylinder barrel are advantageous, in which the cylinder bores and the working pistons are arranged obliquely with respect to the rotational axis of the drive shaft and the inlet openings of the working spaces are arranged radially closer to the rotational axis.
On account of the functional principle of axial piston machines of this type, the cylinder barrel is pressed with a comparatively high force against the stationary control plate, with the result that considerable wear can take place on the bearing faces of the control plate and cylinder barrel during operation of the axial piston machine. In axial piston machines having a planar control plate, in order to reduce said wear, the substantially circularly annular bearing faces are configured as a hydrostatic bearing which is lubricated by operating pressure medium which, as a consequence of the high pressure which is present in the inlet opening of a working space, is driven into the gap which is formed between the bearing faces and contributes to the leakage losses during operation of the axial piston machine. The radial dimensions of the hydrostatic bearing, including the radii of its inner and outer boundaries, are defined by at least one of the bearing faces on the cylinder barrel and the control plate as a circularly annular elevation with a circular inner step and a circular outer step in order to form the inner and outer boundary of the bearing face. A gap is formed during operation between the bearing faces of the hydrostatic bearing, into which gap the operating pressure medium penetrates under the action of the high pressure. Correspondingly, a relieving force which acts on the bearing faces is produced in the hydrostatic bearing in the direction perpendicularly with respect to the respective bearing face. Thus, in the case of a planar control plate with planar, circularly annular bearing faces, a relieving force acts on the cylinder barrel in the axial direction toward the swash plate, as shown in FIGS. 3 to 5. This applies analogously to contact of a cylinder barrel with a spherical control plate, the bearing faces being of spherical configuration. However, in the case of spherical bearing faces, a relieving force which is produced in the spherical gap does not act axially, but rather perpendicularly with respect to the spherical bearing face at an acute angle with respect to the rotational axis of the cylinder barrel, as shown in FIG. 2. The relieving force which acts on the control plate is absorbed by virtue of the fact that, on its side which faces away from the cylinder barrel, the control plate is arranged on the housing of the axial piston machine such that it is supported axially in a pivot bearing. The relieving force which acts on the cylinder barrel is absorbed by the cylinder barrel being mounted rotatably in its swash plate-side end which is opposite to the control plate-side end, in a manner which is supported axially on the housing of the axial piston machine, and being arranged such that it is prestressed axially in the direction of the control plate via a compression spring.
On the foot side, the working pistons are supported on the swash plate. To this end, a piston foot of each working piston is of ball-shaped configuration and is connected in an articulated manner to a piston shoe which slides on the swash plate during rotation of the cylinder barrel. To this end, on the swash plate side, the piston shoe has a planar sliding face which bears in a slidable manner against the swash plate on a lubricating film which is formed by a pressure medium. If a working space is loaded with pressure medium, the working piston is pressed by its piston shoe in the direction of the cylinder bore against the swash plate. The swash plate absorbs this force and, on the sliding face of the piston shoe, a relieving force or counterforce is produced by the piston shoe on the working piston, which relieving force or counterforce acts in a direction perpendicularly with respect to the sliding face or swash plate. If the swash plate is arranged in its basic position, in which the swash plate lies perpendicularly with respect to the rotational axis of the cylinder barrel, the relieving force which is produced on the piston shoe acts on the working piston in the axial direction.
The present disclosure relates to axial piston machines of swash plate design having the configuration which was mentioned at the outset and is disclosed, for example, in GB 1 073 216 or in DE 40 35 748 A1 (FIG. 2), in which configuration the bearing faces of the cylinder barrel and control plate are of planar design and the cylinder bores and the working pistons are arranged obliquely with respect to the rotational axis of the drive shaft. In a configuration of this type, the lines of action of the relieving forces which act on the cylinder barrel are offset with respect to one another on the control plate and on the piston shoe radially with regard to the rotational axis of the cylinder barrel, the relieving force on the control plate being arranged radially closer to the rotational axis, as shown, for example, in FIGS. 3 to 5. A tilting moment which acts on the cylinder barrel is produced on account of the radial offset of the relieving forces on the cylinder barrel at the control plate and at the piston shoe.
In comparison with known axial piston machines in the configuration with bearing faces of planar design of the cylinder drum and control plate and the cylinder bores and working pistons which are arranged obliquely with respect to the rotational axis of the drive shaft, in which the configuration of its driving mechanism has already been optimized with regard to costs, installation space, degree of efficiency, the function and rotational speed which can be achieved of the driving mechanism (approximately 6000 rpm) at a high degree of efficiency, the disclosure is based on the object of providing an axial piston machine, in which the tilting moment which acts on the cylinder barrel as a result of the relieving forces on the control plate and on the piston shoe is small or is avoided.